The Ainu pronunciation of this term has only two morae, so academic materials may spell this term in kana with the small ィ, or in romaji with a y, to explicitly indicate that the initial vowel is the single-mora diphthongay (/ai̯/), and not the two-mora diphthonga i (/a.i/).

However, there is no three-mora term a i nu in the Ainu language, and most Ainu texts written in katakana use the spelling アイヌ instead.